import java.util.Scanner;

/**
 *  圆的面积
 */
public class AreaOfCircle {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        double s = Math.PI * r * r;
        System.out.println(String.format("%.7f",s));
    }
}
